This project continues and extends our ongoing investigations of sexual mixing patterns, partnership types, and STD focusing on subpopulations of special interest. Aim l extends analyses of the association between STD, partnership characteristics, and sexual mixing, both in terms of a new analytic approach with increased emphasis on temporal and functional aspects of partnerships; and in terms of new populations studied including (a) patients with gonococcal or chlamydial infection seen in private health care settings; (b)a comparison of these patients with STD to a sample of Seattle residents recently selected by random digit dialing and interviewed with a questionnaire adapted from that used in STD patients; and (c) men having sex with men (MSM), seen with and without bacterial STD in the STD clinic. Aim 2 will define the influence of individual behaviors, partnership characteristics, and regional factors on STD risk among adolescents and young adults in the US. We will focus on 3 measures of STD, as follows: (a) multi-level model of individual self-reported STD status including individual demographic and behavioral characteristics, partner characteristics, social network position and structure, and STD prevalence and incidence using data from the nationally representative sample of adolescents collected in the National Longitudinal Study of Adolescent Health (n equals approximately 20,745), and from available data on STD morbidity in regionally and demographically defined subpopulations; (b)comparison of the partnerships of adolescents and young adults in the Add Health Study with those attending three urban STD clinics located in the Northwest, Midwest and South, using the Add Health interview instrument; and (c) definition of the prevalence and demographic and behavioral correlates of genital HPV infection in the nationally representative sample of females 17-20 years of age from the Add Health survey. Sexual mixing patterns play a crucial role in the spread of STD in populations. Social networks, partnerships types and attributes of partnerships all influence sexual mixing patterns and are influenced by these patterns. Further insight into these issues would facilitate development of effective interventions and their prioritized implementation, targeting those population groups at high risk for acquiring and transmitting infection. Little is known about adolescents and young adults concerning partnership duration, concurrence of sexual partnerships, structure of sexual and social networks, and partnership types in terms of concordance and discordance. How each of the above relates to spread of specific STDs and varies across sub-populations (e.g. adolescents) and across epidemiologic and social contexts, has important relevance to the design of prevention programs, and could lead to a new focus on promoting healthy partnerships within certain contextual frameworks..